Camshafts of internal combustion engines are generally driven by crankshafts via a chain or a toothed belt and, in the process, are continuously adjusted in a closed control circuit, wherein typical adjustment ranges lie within crank angles of 40 to 60°. Crank angles which can be set are deposited in characteristic diagrams. Adjustments take place, for example, hydraulically, fed from the engine oil circuit via an electrically actuated control valve, and permit optimum valve timings for the engine load and engine speed parameters. Depending on the engine concept and number of adjusters, a significant reduction in fuel consumption and exhaust emissions and an increase in the power and torque can thus be achieved.
DE 42 26 798 A1 discloses an internal combustion engine with a camshaft adjusting system for rotating two concentrically arranged camshaft in order to change phase angles of cams on the first of the concentrically arranged camshafts with respect to the cams on the second of the concentrically arranged camshafts. The two concentrically arranged camshafts are an external shaft and an internal shaft each with cams of identical function, wherein the cams arranged on the internal shaft are mounted on the external shaft and are connected to the internal shaft by a carry-along element configured in the form of a bolt connection. By means of a camshaft adjusting system of this type, it is possible to adjust inlet cams relative to outlet cams without parallel inlet and outlet camshafts, as, for example, in the case of double overhead camshaft (DOHC) engines. A disadvantage of camshaft adjusting systems having two concentrically arranged camshafts is the exacting design required if the rotation of the camshafts is intended to be activated by means of vane cells which require exacting component tolerances and bearing clearances for high adjusting speeds. In a vane cell, the radial clearance between the rotor and stator is restricted to a few hundredth of a millimeter. By connecting the rotor and stator to one of the concentrically arranged camshafts each, the radial position of said rotor and stator with respect to each other is also determined by shape differences and positional differences, in particular by concentricity errors, eccentricities and assembly of the concentrically arranged camshafts. The sum of said differences may be significantly greater than the still permissible, function-determining radial clearance between the rotor and stator. A camshaft adjusting system of this type could jam.